by ʇolɐǝz ǝɥʇ qoq

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In analog photography (film) there was an effect called "Schwartschild effect", or Reciprocity failure when making long exposures (usually more than few seconds).

Some film brands created compensation tables for their films; for instance, you would need to double the time after 4 seconds, meaning if the meter says f/5.6 at 5 seconds you have to expose 10 seconds at the same aperture to get the film correctly exposed.

  1. Does that effect exist in digital photography?

  2. If yes - does the exposure metering automatically compensate for it? (meaning with the above example the exposure time will be automatically adjusted to 10 seconds).

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up vote 9 down vote accepted

Essentially, no - digital sensors are pretty much linear in that if you double the number of photons hitting it, you get double the output. They're obviously not perfectly linear, but they're close enough you don't need to worry about it.

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Thanks for the answer, my feelings was saying the same but I am looking for a technical article which shows (or just mention) that linearity. – ruffp Jun 17 '13 at 20:05

No, the effect does not exist.

However, long exposures in digital have their own host of problems:

  • Sensor overheating. This used to be a bigger problem, but with the advent of video DSLRs this has mostly disappeared.
  • Hot pixels. Some sensors just don't like staying "active" and will internally leak and produce a single color hot pixel. Cameras and software such as Lightroom will automatically remove them, but in very long exposures or night-sky shots, they do not.
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